1. Field of the Invention
The present invention relates to an imaging lens and an imaging apparatus, and more particularly, to an imaging lens suitable for, for example, an in-vehicle camera, a mobile terminal camera, or a monitoring camera using an imaging device, such as a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor), and an imaging apparatus including the imaging lens.
2. Description of the Related Art
In recent years, the size of an imaging device, such as a CCD or a CMOS, has been reduced, and the number of pixels thereof has increased. In addition, the size of the imaging apparatus including the imaging device has been reduced. Therefore, it is necessary to improve the optical performance of an imaging lens provided in the imaging apparatus and to reduce the size and weight of the imaging lens.
Meanwhile, for example, an in-vehicle camera or a monitoring camera requires a high-performance lens that has high weather resistance, that can be used in a wide temperature range in a vehicle from a low temperature in a cold region to a high temperature in a tropical region, and that has a small size and a high performance. In particular, a camera that is provided in a vehicle and that monitors the front side thereof needs to have such a small F number that it can be used at night and be used in a wide wavelength band from a visible range to an infrared range. When the imaging apparatus is used as an in-vehicle camera, a small portion of a lens unit needs to be exposed in terms of the outward appearance of the vehicle.
JP-A-2008-287045 filed by the inventors discloses an imaging lens that can be used in the above-mentioned field. In addition, JP-A-55-45007, JP-A-61-90115, JP-A-9-230232, and JP-A-2005-164839 disclose imaging lenses each having a six-lens structure. The image lens disclosed in JP-A-55-45007 includes a negative lens, a positive lens, a positive lens, an aperture diaphragm, a negative lens, a positive lens, and a positive lens arranged in this order from an object side. The imaging lens disclosed in JP-A-61-90115 includes a negative lens, a positive lens, a positive lens, an aperture diaphragm, a negative lens, a positive lens, and a negative lens arranged in this order from an object side. The imaging lens disclosed in JP-A-9-230232 includes a negative lens, a positive lens, an aperture diaphragm, a positive lens, a negative lens, a positive lens, and a positive lens arranged in this order from an object side. The imaging lens disclosed in the JP-A-2005-164839 includes a negative lens, a positive lens, a positive lens, an aperture diaphragm, a negative lens, a positive lens, and a positive lens arranged in this order from an object side.
However, since it is considered that the in-vehicle camera or the monitoring camera is to be used at night, an optical system having a small F number is required. However, the imaging lenses disclosed in JP-A-55-45007 and JP-A-61-90115 have a large F number in the range of 3.3 to 4.5 and become so-called slow optical systems, which is not preferable. Since the imaging lens disclosed in JP-A-2005-164839 has an F number of 2.5, the F number of the imaging lens needs to be reduced. In addition, since an aspheric lens is used, the imaging lens has a high manufacturing cost.
The imaging lens disclosed in JP-A-2008-287045 has an angle of view of about 27°. Therefore, it is preferable to increase the angle of view of the imaging lens in order to use it for an in-vehicle camera or a monitoring camera.